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Topic Page
Introduction
Acknowledgements
Contact Process
Haber Process
Alloy
Polymer
Glass
Reference
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Contact process
y trioxide into concentrated sulphuric acid.
y The contact process is the current method of producing sulfuric acid in
the high concentrations needed makes sulphur dioxide;
y convers the sulphur dioxide into sulphur trioxide (the reversible reaction
at the heart of the process);
converts the sulphur for industrial processes. Platinum was formerly employed
as a catalyst for the reaction, but as it is susceptible to poisoning by arsenic
impurities in the sulfur feedstock, vanadium(V) oxide (V2O5) is now preferred[1]
.
This process was patented in 1831 by the British vinegar merchant Peregrine
Phillips. In addition to being a far more economical process for producing
concentrated sulfuric acid than the previous lead chamber process, the contact
process also produces sulfur trioxide and oleum Making the sulphur dioxide
This can either be made by burning sulphur in an excess of air:
. . . or by heating sulphide ores like pyrite in an excess of air:
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In either case, an excess of air is used so that the sulphur dioxide produced is
already mixed with oxygen for the next stage.
C onverting the sulphur dioxide into sulphur trioxide
This is a reversible reaction, and the formation of the sulphur trioxide is
exothermic.
A flow scheme for this part of the process looks like this: (next page)
C onverting the sulphur trioxide into sulphuric acid
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T his can't be done by simply adding water to the sulphur trioxide - the reaction is so
uncontrollable that it creates a fog of sulphuric acid. Instead, the sulphur trioxide is first
dissolved in concentrated sulphuric acid:
T he product is known as fuming sulphuric acid or oleum.
T his can then be reacted safely with water to produce concentrated sulphuric acid - twice as
much as you originally used to make the fuming sulphuric acid.
The process can be divided into three stages :
1. Preparation and purification of sulfur dioxide
2. Catalytic oxidation (using vanadium pentoxide catalyst) of sulfur dioxide
to sulfur trioxide
3. Conversion of sulfur trioxide to sulfuric acid
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DCDA
The next step to the Contact Process is DCDA or Double Contact
Double Absorption. In this process the product gases (SO2) and (SO3)
are passed through absorption towers twice to achieve further
absorption and conversion of SO2 to SO3 and production of higher
grade sulfuric acid.
SO2 rich gases enter the catalytic converter, usually a tower with
multiple catalyst beds, and get converted to SO3, achieving the first
stage of conversion. The exit gases from this stage contain both SO2
and SO3 which are passed through intermediate absorption towers
where sulfuric acid is trickled down packed columns and SO3 reacts
with water increasing the sulfuric acid concentration. Though SO2 too
passes through the tower it is unreactive and comes out of the
absorption tower.
This stream of gas containing SO2, after necessary cooling is passed
through the catalytic converter bed column again achieving up to 99.8%
conversion of SO2 to SO3 and the gases are again passed through the
final absorption column thus resulting not only achieving high
conversion efficiency for SO2 but also enabling production of higher
concentration of sulfuric acid.
The industrial production of sulfuric acid involves proper control of
temperatures and flow rates of the gases as both the conversion
efficiency and absorption are dependent on these.
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Haber Process
Sometimes called the most important technological advance of this century, the
Haber -Bosch process allows the economical mass synthesis of ammonia (NH3)
from nitrogen and hydrogen. It was developed immediately prior to World War
I by Fritz Haber and Carl Bosch, German chemists. Haber won the Nobel Prize
for Chemistry in 1918 for his discoveries, while Bosch shared a Nobel Prize
with Friedrich Bergius in 1931 for his work on high-pressure chemical reactions.
At first a German national secret, the chemistry and techniques behind the
effective synthesis of ammonia spread to the rest of the world in the 20s and 30s.
Ammonia is important because it is the primary ingredient in artificial fertilizers,
without which modern-day agricultural yields would be impossible. Sometimes
called the "Haber Ammonia process," the Haber-Bosch process was the first
industrial chemical process to make use of extremely high pressures (200 to 400
atmospheres). In addition to high pressures, high temperatures (75 0 to 1200
degrees Fahrenheit or 400 to 650 degrees Celsius) are used. The efficiency of
the reaction is a function of pressure and temperature - greater yields are
produced at higher pressures and lower temperatures.
In the first decade of the 20th century, the artificial synthesis of nitrates was
being researched because of fears that the world's supply of fixed nitrogen was
declining rapidly relative to the demand. While nitrogen in its inactive,
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atmospheric gas form is very plentiful, agriculturally useful "fixed" nitrogen
compounds were harder to come by at that time in history. Agricultural
operations require liberal amounts of fixed nitrogen to produce good yields. At
the turn of the century, all the world's developed countries were required to
mass import nitrates from the largest available source - Chilean saltpeter
(NaNO3). Many scientists started worrying about the declining supply of
nitrogen compounds.
The Haber-Bosch process provided a solution to the shortage of fixed nitrogen.
Using extremely high pressures and a catalyst composed mostly of iron, critical
chemicals used in both the production of fertilizers and explosives, we re made
highly accessible to German industry, making it possible for them to continue
fighting WWI effectively. As the Haber-Bosch process branched out in global
use, it became the primary procedure responsible for the production of chemical
fertilizers. Today, the Haber-Bosch process is used to produce more than 500
million tons (453 billion kilograms) of artificial fertilizer per year; roughly 1%
of the world's energy is used for it, and it sustains about 40% of our planetary
population.The Haber Process combines nitrogen from the air with hydrogen
derived mainly from natural gas (methane) into ammonia.
The reaction is reversible and the production of ammonia is exothermic.
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A flow scheme for the Haber Process looks like this:
The proportions of nitrogen and hydrogen
The mixture of nitrogen and hydrogen going into the reactor is in the ratio of 1
volume of nitrogen to 3 volumes of hydrogen.
Avogadro's Law says that equal volumes of gases at the same temperature and
pressure contain equal numbers of molecules. That means that the gases are
going into the reactor in the ratio of 1 molecule of nitrogen to 3 of hydrogen.
That is the proportion demanded by the equation.
In some reactions you might choose to use an excess of one of the rea ctants.
You would do this if it is particularly important to use up as much as possible of
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the other reactant - if, for example, it was much more expensive. That doesn't
apply in this case.
There is always a down-side to using anything other than the equat ion
proportions. If you have an excess of one reactant there will be molecules
passing through the reactor which can't possibly react because there isn't
anything for them to react with. This wastes reactor space - particularly space
on the surface of the catalyst
When the gases leave the reactor they are hot and at a very high
pressure. Ammonia is easily liquefied under pressure as long as it isn't
too hot, and so the temperature of the mixture is lowered enough for
the ammonia to turn to a liquid. The nitrogen and hydrogen remain as
gases even under these high pressures, and can be recycled.
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The Properties of Ammonia :
-colourless and pungent gas
-alkaline gas
-soluble in water
-reacts with Hydrogen chloride to form white fumes of ammonia chloride
NH3+HCL=>NH4CL
-reacts with dilute acid to produce salt.
The Uses of Ammonia :
-manufacture of nitric acid
-manufacture of explosives
- as a cooling agentin refrigerators
-as an alkali to prevent coagulation of latex
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Alloys
An alloy is a partial or complete solid solution of one or more elements in a
metallic matrix. Complete solid solution alloys give single solid phase
microstructure, while partial solutions give two or more phase s that may be
homogeneous in distribution depending on thermal (heat treatment) history.
Alloys usually have different properties from those of the component el ements.
Alloys' constituents are usually measured by mass.
A pure metal(alloy) has the following characteristics:
p Ductile- can be drawn to wires
p Malleable- can be made into sheets
p High melting and boiling points
p High density
p High electric conductivity
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Properties
The malleability and acoustic properties of brass have made it the metal of
choice for brass musical instruments such as the trombone, tuba, trumpet, cornet,
euphonium, tenor horn, and the French horn. ven though the saxophone is
classified as a woodwind instrument and the harmonica is a free reed aerophone,
both are also often made from brass. In organ pipes of the reed family, brass
strips (called tongues) are used as the reeds, which beat against the shallot (or
beat "through" the shallot in the case of a "free" reed).
Brass has higher malleability than copper or zinc. The relatively low melting
point of brass (900 to 940°C, depending on composition) and its flow
characteristics make it a relatively easy material to cast. By varying the
proportions of copper and zinc, the properties of the brass can be changed,
allowing hard and soft brasses. The density of brass is approximately 8400 to
8730 kilograms per cubic metre[11]
(equivalent to 8.4 to 8.73 grams per cubic
centimetre).
Today almost 90% of all brass alloys are recycled.[12]
Because brass is not
ferromagnetic, it can be separated from ferrous scrap by passing the scrap near a
powerful magnet. Brass scrap is collected and transported to the foundry where
it is melted and recast into billets. Billets are heated and extruded into the
desired form and size.
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Aluminium makes brass stronger and more corrosion resistant. Aluminium also
causes a highly beneficial hard layer of aluminium oxide (Al2O3) to be formed
on the surface that is thin, transparent and self healing. Tin has a similar effect
and finds its use especially in sea water applications (naval brasses).
Combinations of iron, aluminium, silicon and manganese make brass wear and
tear resistant
Alloy(bronze)
Alloy traditionally composed of copper and tin. Bronze was first made before
3000 BC ( see Bronze Age) and is still widely used, though iron often replaced
bronze in tools and weapons after about 1000 BC because of iron's abundance
compared to copper and tin. Bronze is harder than copper, more readily melted,
and easier to cast. It is also harder than iron and far more resistant to corrosion.
Bell metal (which produces pleasing sounds when struck) is bronze with 20
25% tin content. Statuary bronze, with less than 10% tin and an admixture of
zinc and lead, is technically a brass. The addition of less than 1% phosphorus
improves the hardness and strength of bronze; that formulation is used for pump
plungers, valves, and bushings. Also useful in mechanical engineering are
manganese bronzes, with little or no tin but considerable amounts of zinc and up
to 4.5% manganese. Aluminum bronzes, containing up to 16% aluminum and
small amounts of other metals such as iron or nickel, are especially strong and
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corrosion-resistant; they are cast or wrought into pi pe f ittings, pumps, gears,
shi p propellers, and turbine blades. Most "copper " coins are actually bronze,
typically with about 4% tin and 1% zinc, or copper plating over base metal
Ass
¡
ted ancient bronze castings
Proper ties
Bronze is considerably less br ittle than iron. Typically bronze only oxidizes
superf icially; once a copper oxide (eventually becoming copper carbonate) layer
is formed, the under lying metal is protected from fur ther corrosion. However, if
copper chlor ides are formed, a corrosion-mode called " bronze disease" will
eventually completely destroy it.[10]
Copper-based alloys have lower melting
points than steel or iron, and are more readily produced from their constituent
metals. They are generally about 10 percent heavier than steel, although alloys
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using aluminium or silicon may be slightly less dense. Bronzes are softer and
weaker than steel²bronze springs, for example, are less stiff (and so store less
energy) for the same bulk. Bronze resists corrosion (especially seawater
corrosion) and metal fatigue more than steel and is also a better conductor of
heat and electricity than most steels. The cost of copper -base alloys is generally
higher than that of steels but lower than that of nickel-base alloys.
Copper and its alloys have a huge variety of uses that reflect their versatile
physical, mechanical, and chemical properties. Some common examples are the
high electrical conductivity of pure copper, the excellent deep drawing qualities
of cartridge case brass, the low-friction properties of bearing bronze, the
resonant qualities of bell bronze, and the resistance to corrosion by sea water of
several bronze alloys.
The melting point of Bronze varies depending on the actual ratio of the alloy
components and is about 950 °C.
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Alloys(Duralumin)
(also called duraluminum, duraluminium or dural) is the trade name of one of
the earliest types of age-hardenable alloys. The main alloying constituents are
copper , manganese, and magnesium. A commonly used modern equivalent of
this alloy type is AA2024, which contains 4.4% copper, 1. 5% magnesium, 0.6%
manganese and 93.5% aluminium by weight. Typical yield strength is 450 MPa,
with variations depending on the composition and temper .[1]
Duralumin was developed by the German metallurgist Alfred Wilm at Dürener
Metallwerke Aktien Gesellschaft. In 1903, Wilm discovered that after
quenching, an aluminium alloy containing 4% copper would slowly harden
when left at room temperature for several days. Further improvements led to the
introduction of duralumin in 1909.[2]
The name is obsolete today, and mainly
used in popular science to describe the Al-Cu alloy system, or 2000 series as
designated by the International Alloy Designation System (IADS) originally
created in 1970 by the Aluminum Association.
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Its f irst use was r igid airshi p frames. Its composition and heat treatment were a
war time secret. With this new r i p-resistant mixture, duralumin quick ly spread
throughout the aircraf t industry in the ear ly 1930s, where it was well suited to
the new monocoque construction techniques that were being introduced at the
same time. Duralumin also is popular for use in precision tools such as levels
because of its light weight and strength.
Although the addition of copper improves strength, it also makes these alloys
suscepti ble to corrosion. For sheet products, corrosion resistance can be greatly
enhanced by metallurgical bonding of a high-pur ity aluminium surface layer.
These sheets are referred to as alclad, and are commonly used by the aircraf t
industry.[3]
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Alloys(stainless steel)
Stainless steel is an iron-containing alloy²a substance made up of two or more
chemical elements²used in a wide range of applications. It has excellent
resistance to stain or rust due to its chromium content, usually from 12 to 20
percent of the alloy. There are more than 57 stainless steels recognized as
standard alloys, in addition to many proprietary alloys produced by different
stainless steel producers. These many types of steels are used in an almost
endless number of applications and industries: bulk materials handling
equipment, building exteriors and roofing, automobile components (exhaust,
trim/decorative, engine, chassis, fasteners, tubing for fuel lines), chemical
processing plants (scrubbers and heat exchangers), pulp and paper
manufacturing, petroleum refining, water supply piping, consumer products,
marine and shipbuilding, pollution control, sporting goods (snow skis), and
transportation (rail cars), to name just a few.
About 200,000 tons of nickel-containing stainless steel is used each year by the
food processing industry in North America. It is used in a variety of food
handling, storing, cooking, and serving equipment ²from the beginning of the
food collection process through to the end. Beverages such as milk, wine, beer,
soft drinks and fruit juice are processed in stainless steel equipment. Stainless
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steel is also used in commercial cookers, pasteurizers, transfer bins, and other
specialized equipment. Advantages include easy cleaning, good corrosion
resistance, durability, economy, food flavor protection, a nd sanitary design.
According to the U.S. Department of Commerce, 1992 shipments of all stainless
steel totaled 1,514,222 tons.
Stainless steels come in several types depending on their microstructure.
Austenitic stainless steels contain at least 6 percent nickel and austenite ²
carbon-containing iron with a face-centered cubic structure²and have good
corrosion resistance and high ductility (the ability of the material to bend
without breaking). Ferritic stainless steels (ferrite has a body -centered cubic
structure) have better resistance to stress corrosion than austenitic, but they are
difficult to weld. Martensitic stainless steels contain iron having a needle-like
structure.
Duplex stainless steels, which generally contain equal amounts of ferrite and
austenite, provide better resistance to pitting and crevice corrosion in most
environments. They also have superior resistance to cracking due to chloride
stress corrosion, and they are about twice as strong as the common austenitics.
Therefore, duplex stainless steels are widely used in the chemical industry in
refineries, gas-processing plants, pulp and paper plants, and sea water piping
installations.
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Stainless steels are made of some of the basic elements found in the earth: iron
ore, chromium, silicon, nickel, carbon, nitrogen, and manganese. Properties of
the final alloy are tailored by varying the amounts of these elements. Nitrogen,
for instance, improves tensile properties like ductility. It also improves
corrosion resistance, which makes it valuable for use in duplex stainless steels.]
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Polymer
a chemical compound of high molecular weight (from several thousand up to
many millions), whose molecules (macromolecules) consist of a large number
of repeating groups, or monomeric units. The atoms composing the
macromolecules are bound on one another by regular and/or coordinate bonds.
Polymers are classified according to origin as natural polymers, or biopolymers
(for example, proteins, nucleic acids, and natur al resins), and synthetic polymers
(polyethylene, polypropylene, and phenol -formaldehyde resins). The atoms or
atomic groups may be arranged in an open chain or a sequence of consecutive
rings (linear polymers, such as natural rubber), a branched chain (am ylopectin),
or a three-dimensional network (crosslinked polymers, such as solid epoxy
resins). Polymers consisting of identical monomer units²for example,
polyvinyl chloride, polycaproamide, and cellulose ²are called homopo-lymers.
Properties and most important characteristics. Linear polymers have a
specific set of physicochemical and mechanical properties. The most important
properties are the ability to form high-strength anisotropic, highly oriented
fibers and films; the capacity for large, slowly devel oping reversible
deformations; the ability to swell in the hyperelastic state before dissolving; and
the high viscosity of solutions. This set of properties results from the high
molecular weight, the chain structure, and the flexibility of the macromolecu les.
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In the transition from linear to branched, sparse three-dimensional networks,
and finally to dense cross-linked structures, these properties become
decreasingly pronounced. Strongly crosslinked polymers are insoluble, infusible,
and incapable of hyperelastic deformations.
Polymers may exist in the crystalline and amorphous states. A necessary
condition for crystallization is regularity of sufficiently long segments of the
macromolecule. Various textures, such as fibrils, spheroidal aggregates, and
single crystals, may arise in crystalline polymers, depending largely on the
properties of the polymer material. Textures are less pronounced in amorphous
polymers than in crystalline polymers.
Synthetic polymers are often referred to as " plastics", such as the well-known
polyethylene and nylon. However, most of them can be classified in at least
three main categories: thermoplastics, thermosets and elastomers.
Man-made polymers are used in a wide array of applications: food packaging,
films, fibers, tubing, pipes, etc. The personal care industry also uses polymers to
aid in texture of products, binding, and moisture retention (e.g. in hair gel and
conditioners).
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Polyethylene-Polyethylene is a polymer consisting of long chains of the
monomer ethylene (IUPAC name ethene). The recommended scientific name
polyethene is systematically derived from the scientific name of the
monomer.[1][2]
In certain circumstances it is useful to use a structure based
nomenclature. In such cases IUPAC recommends poly(methylene).[2]
The
difference is due to the opening u p of the monomer's double bond upon
polymerisation.
In the polymer industry the name is sometimes shortened to PE in a manner
similar to that by which other polymers like polypropylene and polystyrene are
shortened to PP and PS respectively. In the United Kingdom the polymer is
commonly called polythene, although this is not recognised scientifically.
The ethene molecule (known almost universally by its common
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Glass
(non-crystalline) solid material. Glasses are typically brittle, and often optically
transparent. Glass is commonly used for windows, bottles, and eyewear ;
examples of glassy materials include soda-lime glass, borosilicate glass, acrylic
glass, sugar glass, Muscovy-glass, and aluminium oxynitride. The term g la ss
developed in the late Roman mpire. It was in the Roman glassmaking center at
Trier , now in modern Germany, that the late-Latin term g l esum originated,
probably from a Germanic word for a transparent, lustrous substance.[1]
Strictly speaking, a glass is defined as an inorganic product of fusion which has
been cooled through its glass transition to the solid state without
crystallising.[2][3][4][5][6]
Many glasses contain silica as their main component and
g la ss f or mer .
[7]
The term "glass" is, however, often extended to all amorphous
solids (and melts that easily form amorphous solids), including plastics, resins,
or other silica-free amorphous solids. In addition, besides traditional melting
techniques, any other means of preparatio n are considered, such as ion
implantation, and the sol-gel method.[7]
Commonly, g la ss science and physics
deal only with inorganic amorphous solids, while plastics and similar organics
are covered by polymer science, biology and further scientific disciplines.
Glass plays an essential role in science and industry. The optical and physical
properties of glass make it suitable for applications such as flat glass, container
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glass, optics and optoelectronics material, laboratory equipment, thermal
insulator (glass wool), reinforcement fiber (glass-reinforced plastic, glass fiber
reinforced concrete), and art.
Glass(soda lime)
Soda-lime glass, also called soda-lime-silica glass, is the most prevalent type
of glass, used for windowpanes, and glass containers (bottles and jars) for
beverages, food, and some commodity items. Glass bakeware is often made of
tempered soda-lime glass.[1]
Soda-lime glass is prepared by melting the raw materials, such as sodium
carbonate (soda), lime, dolomite, silicon dioxide (silica), aluminium oxide
(alumina), and small quantities of fining agents (e.g., sodium sulfate, sodium
chloride) in a glass furnace at temperatures locally up to 1675 °C.
[2]
The
temperature is only limited by the quality of the furnace superstructure material
and by the glass composition. Green and brown bottles are obtained from raw
materials containing iron oxide. Relatively inexpensive minerals such as trona,
sand, and feldspar are used instead of pure chemicals. The mix of raw materials
is termedbatch.
Soda-lime glass is divided technically into glass used for windows, called f loat
g la ss or f lat g la ss, and glass for containers, called cont ainer g la ss. Both types
differ in the application, production method ( float process for windows, blowing
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and pressing for containers), and chemical composition (see table below). Float
glass has a higher magnesium oxide and sodium oxide content as compared to
container glass, and a lower silica, calcium oxide, and aluminium oxide
content.[3]
From this follows a slightly higher quality of container glass
concerning the chemical durability against water (see table), which is required
especially for storage of beverages and food.
Glass(borosilicate)
is a type of glass with the main glass-forming constituents silica and boron
oxide. Borosilicate glasses are known for having very low coefficients of
thermal expansion (~5 × 10í6
/°C at 20°C), making them resistant to thermal
shock , more so than any other common glass. Borosilicate glass has a very low
thermal expansion coefficient, about one-third that of ordinary glass. This
reduces material stresses caused by temperature gradients, thus making it more
resistant to breaking. This makes it a popular material for objects like telescope
mirrors, where it is essential to have very little deviation in shape. It is also used
in the processing of high-level radioactive waste, where the waste is
immobilised in the glass through a process known as vitrification (contrast with
Synroc).
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The softening point (temperature at which viscosity is approximately 107.6
poise)
of type 7740 Pyrex is 820 °C (1,510 °F).[4]
Borosilicate glass is less dense than ordinary glass.
While more resistant to thermal shock than other types of glass, borosilicate
glass can still crack or shatter when subject to rapid or uneven temperature
variations. When broken, borosilicate glass tends to crack into large pieces
rather than shattering (it will snap rather than splinter).
Optically, borosilicate glasses are crown glasses with low dispersion (Abbe
numbers around 65) and relatively low refractive indices (1.51 1.54 across the
visible range).